C++ initalize class values after constructor

Question

I have a class like this:

class test{
private:
    anotherClass _someVar;
public:

    test(){}; 

    void load() {
        anotherClass _someVar = anotherClass(.....);
    }
};

But this keeps getting the error no default constructor exists for class "anotherClass". But if I move the function load() into the constrcutor I also get the same error.

class test{
private:
    anotherClass _someVar;
public:

    test(){
        anotherClass _someVar = anotherClass(.....);
    }; 

};

Lastly, if this is illegal in c++, is there a way I can generate a class variable within a function of that class that can be shared to other functions of that same class? For that specific instance that is.